Thermally efficient battery cell assembly

ABSTRACT

A battery cell assembly, including a rolled cell formed from a first electrode and a second electrode rolled together about a longitudinal axis. The rolled cell includes a primary section in which the first electrode and the second electrode overlap in a radial direction from the longitudinal axis, and a first extension end extending from a first longitudinal end of the primary section and formed from a first edge section of the first electrode. The first edge section includes a first folded portion folded to contact an adjacent portion of the first edge section. The battery cell assembly further includes a first end cap coupled to the rolled cell and contacting the first folded portion.

BACKGROUND

Lithium-ion batteries are becoming more prevalent as many vehicles thathave traditionally been powered by combustion engines now incorporatebattery-powered electric engines. Lithium-ion batteries have a lithiummetal oxide cathode and a graphite anode, between which lithium ionspass. During charging, electrons are provided to the anode and lithiumions travel from the cathode to the anode to unite with the electrons.During discharging, when a load is applied to the battery, the electronstravel through the load (providing current to the load) to the cathodeand the lithium ions travel back to the cathode to reunite with theelectrons.

In some designs, lithium-ion batteries incorporate tabs for transferringcurrent between an active part of the battery and the load. When largeloads are applied, passing the required current through the small tabcan cause batteries to overheat. Additionally, lithium-ion batteries aretypically encased in a metallic jacket, which can add a significantamount of weight to the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an oblique view of an aircraft according to anembodiment of this disclosure.

FIG. 2 illustrates an oblique view of a battery of the aircraft of FIG.1 according to an embodiment of this disclosure with part of the jacketand an end cap removed to show the battery cell.

FIG. 3 illustrates an oblique view of a battery cell of the battery ofFIG. 2 in an unrolled state.

FIG. 4 illustrates a side view of a battery cell of the battery of FIG.2 in an unrolled state.

FIG. 5 illustrates a cutaway view of a battery cell of the battery ofFIG. 2 in a rolled state.

FIG. 6 illustrates a cross-sectional view of the battery of FIG. 2.

FIG. 7 illustrates an oblique view of a battery of the aircraft of FIG.1 according to another embodiment of this disclosure with part of thejacket and an end cap removed to show the battery cell.

FIG. 8 is a flowchart illustrating a method of assembling a batteryaccording to an embodiment of this disclosure.

FIG. 9 is a flowchart illustrating a method of assembling a battery witha flexible jacket according to an embodiment of this disclosure.

FIG. 10 is a flowchart illustrating a method of assembling a batterywith a rigid jacket according to an embodiment of this disclosure.

DETAILED DESCRIPTION

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

FIG. 1 illustrates an oblique view of a tailsitter unmanned aerialvehicle (“UAV”) 100 operable to transition between thrust-borne lift ina vertical takeoff and landing (“VTOL”) orientation and wing-borne liftin a biplane orientation. In some embodiments, UAV 100 is a BellAutonomous Pod Transport (“APT”) aircraft. In the VTOL orientation,thrust modules 102 provide thrust-borne lift and, in the biplaneorientation, thrust modules 102 provide forward thrust and the forwardairspeed of UAV 100 provides wing-borne lift. Thrust modules 102 aremounted to wings 104, which generate lift responsive to forward airspeedwhen the UAV 100 is in the biplane orientation. Wings 104 are mounted toa payload 106 of UAV 100 by trusses 108. Each thrust module 102 includesa rotor assembly 110 with propellers 112 configured to rotate to providethrust and direct ram air and propeller wash toward thrust module 102.Each of the thrust modules 102 includes an electric motor 114 fordriving rotor assembly 110 and a battery pack 116 configured to provideelectrical energy to motor 114.

FIG. 2 illustrates a battery cell assembly 200 according to anembodiment of this disclosure. Battery pack 116 can include one or morebatteries 200 to power rotor assembly 110. Battery pack 116 can containa plurality of batteries 200 connected in series or in parallel toincrease the output thereof. Battery 200 has a jacket 202 containing abattery cell 204 and electrode end caps 206, 208. As will be discussedin greater detail below, jacket 202 is made from a non-conductivematerial. As will be discussed in greater detail below, one of electrodeend caps 206, 208 contacts a positive electrode of battery cell 204 andthe other one of electrode end caps 206, 208 contacts a negativeelectrode of battery cell 204. Accordingly, end caps 206, 208 can beelectrically connected to a circuit to supply electrical energy to anelectronic load of motor 114.

Battery cell 204 is a cylindrically-shaped battery cell, commonlyreferred to as a jelly roll design. Referring to FIGS. 3 and 4, batterycell 204 has two electrodes 210, 212, separated by an inner separator214, and an outer separator 216. Specifically, electrode 210 is anegative electrode, which can also be referred to as an anode, andelectrode 212 is a positive electrode, which can also be referred to asa cathode. Cathode 212 can be made of any lithium metal oxide materialtypically used in lithium-ion batteries, such as, for example, LithiumCobalt Oxide, Lithium Manganese Oxide, Lithium Iron Phosphate, LithiumNickel Manganese Cobalt, or Lithium Nickel Cobalt Aluminum Oxide. Anode210 can be made of any material typically used in lithium-ion batteries,such as, for example, graphite. In some embodiments, battery 200 can bea lithium-silicon battery and can comprise a lithium cathode 212 and asilicon anode 210. In some embodiments, battery 200 can be alithium-sulfur battery and can comprise a sulfur cathode 212 and alithium anode 210. Separators 214, 216 are positioned between anode 210and cathode 212 to prevent electrical shorts, and also prevent dendriteformations from forming between electrodes 210, 212. FIGS. 3 and 4illustrate the components of battery cell 204 before the variouscomponents are wound about axis 218 to form the cylindrically-shapedjelly roll design. After cell 204 is wound to its cylindrical shape,part of outer separator 216 is disposed between anode 210 and cathode212 (for example, as in FIG. 5). Separators 214, 216 can be made fromany material typically used in batteries. In some embodiments,separators 214, 216 can be made from a polymer material, such as, forexample, polyethylene or polypropylene.

Referring to FIGS. 4 and 5, the various components of cell 204 arelayered to form a primary section 220, an anode extension end 222, and acathode extension end 224. In primary section 220, anode 210, cathode212, and both separators 214, 216 overlap in a direction 225perpendicular to longitudinal axis 218 about which cell 204 is wound. Anedge of anode 210 and an edge of outer separator 216 extend from primarysection 220 and are disposed in anode extension end 222, while cathode212 and inner separator 214 do not extend into anode extension end 222.Accordingly, anode 210 and outer separator 216 overlap along direction225 in anode extension end 222. An edge of cathode 212 and an edge ofinner separator 214 extend from primary section 220 and are disposed incathode extension end 224, while anode 210 and outer separator 216 donot extend into cathode extension end 224. Accordingly, cathode 212 andinner separator 214 overlap along direction 225 in cathode extension end224.

Although the drawings illustrate that outer separator 216 extends intoanode extension end 222 and that inner separator 214 extends intocathode extension end 224, one with skill in the art will recognize thatother embodiments are possible. For example, in some embodiments, outerseparator 216 extends into cathode extension end 224 and inner separator214 extends into anode extension end 222. In some embodiments, bothseparators 214, 216 extend into anode extension end 222 and cathodeextension end 224. In some embodiments, neither of the separators 214,216 extend into either anode extension end 222 or cathode extension end224.

Referring to FIG. 6, a cross-sectional view of battery 200 isillustrated. End cap 206 is coupled to anode extension end 222 and thuscan be referred to as an anode end cap 206. Similarly, end cap 208 iscoupled to cathode extension end 224 and thus can be referred to as acathode end cap 208. End caps 206, 208 are made from a conductivematerial, and current can pass between anode end cap 206 and anode 210,and between cathode end cap 208 and cathode 212. Accordingly, end caps206, 208 can be electrically coupled to a circuit to supply electricalenergy to a load of motor 114.

An edge of anode 210 disposed in anode extension end 222 has a pluralityof folded portions 226. As illustrated, distal ends of the foldedportions 226 can be folded inward, toward axis 218. However, in someembodiments, one or more folded portions 226 are folded outward, awayfrom axis 218. Additionally, an edge of outer separator 216 disposed inanode extension end 222 has a plurality of folded portions 228. Anodefolded portion 226 is folded such that a separator folded portion 228 isdisposed between the anode folded portion 226 and primary section 220.Specifically, separator folded portion 228 is disposed to preventcontact between anode folded portion 226 and an edge of cathode 212adjacent to anode extension end 222. As previously discussed, contactbetween anode 210 and cathode 212 could lead to shorting or dendriteformation, and folded portion 228 is positioned to prevent such contactfrom occurring. Additionally, anode folded portion 226 can be folded tocontact an adjacent portion of anode 210. In some embodiments, a distaledge of anode folded portion 226 contacts an adjacent anode foldedportion 226. In some embodiments, an inward-facing surface of foldedportion 226 (a surface of folded portion 226 facing primary section 220)contacts an outward facing surface of an adjacent folded portion 226such that adjacent folded portions 226 overlap along longitudinal axis218.

Similarly, an edge of cathode 212 disposed in cathode extension end 224has a plurality of folded portions 230. As illustrated, distal ends ofthe folded portions 230 can be folded inward, toward axis 218. However,in some embodiments, one or more folded portions 230 are folded outward,away from axis 218. Additionally, an edge of inner separator 214disposed in cathode extension end 224 has a plurality of folded portions232. Cathode folded portion 230 is folded such that a separator foldedportion 232 is disposed between the cathode folded portion 230 andprimary section 220. Specifically, separator folded portion 232 isdisposed to prevent contact between cathode folded portion 230 and anedge of anode 210 adjacent to cathode extension end 224. As previouslydiscussed, contact between anode 210 and cathode 212 could lead toshorting or dendrite formation, and folded portion 232 is positioned toprevent such contact from occurring. Additionally, cathode foldedportion 230 can be folded to contact an adjacent portion of cathode 212.In some embodiments, a distal edge of cathode folded portion 230contacts an adjacent cathode folded portion 230. In some embodiments, aninward-facing surface of folded portion 230 (a surface of folded portion230 facing primary section 220) contacts an outward facing surface of anadjacent folded portion 230 such that adjacent folded portions 230overlap along longitudinal axis 218.

In some embodiments, the edge of electrode 210, 212 disposed inextension end 222, 224 may incorporate slits substantially parallel withlongitudinal axis 218 to further define folded portions 226, 230.However, in other embodiments, folded portions 226, 230 are foldedwithout the use of the described slits. That is to say, in someembodiments, the edge of electrode 210, 212 disposed in extension end222, 224 is a continuous piece of material.

Folded portions 226, 230 increase the geometrical contact surface areabetween each electrode 210, 212 and its respective end cap 206, 208.Current transfer between each electrode 210, 212 and its respective endcap 206, 208 is improved due to the increase of contact surface area.Heat transfer of battery 200 is also improved due to current efficientlybeing transferred between the electrode 210, 212 and its respective endcaps 206, 208. In some embodiments, folded portions 226, 230 form agenerally circular surface area through which current can travel betweenelectrode 210, 212 and end cap 206, 208.

In some embodiments, surface treatment processes can be applied to endcaps 206, 208 and/or folded portions 226, 230 to further increase thecontact surface area through which current can travel. Surfaces offolded portions 226, 230 and/or inner surface 234, 236 can be surfacesthat have undergone a subtractive surface treatment process or anadditive treatment process to increase the surface area through whichcurrent can transfer. Subtractive surface treatment processes increaseconductive surface area by removing part of the processed surface. Anexample of subtractive surface treatment processes is acid etching,which removes material from the processed surface area at the nano leveland thus increases the surface area through which a current can pass.When folded portion 226, 230 and/or inner surface 234, 236 are acidetched surfaces, the total contact surface area between the foldedportion 226, 230 and its respective end cap 206, 208 through whichcurrent can pass is even greater than the geometrical surface area, and,thus, current transfer and heat transfer is further improved.

Additive surface treatment processes increase conductive surface area byadding material to the processed surface. After applied, the additivematerial can have a surface with more irregularities at the nano levelthan the surface to which it was applied, thus increasing the surfacearea through which a current can pass. When folded portions 226, 230and/or inner surfaces 234, 236 are subjected to an additive surfacetreatment process, the total contact surface area between the foldedportion 226, 230 and its respective end cap 206, 208 through whichcurrent can pass is even greater than the geometrical surface area, and,thus, current transfer and heat transfer is further improved. Additivesurface treatments can be performed using any of a variety of suitableprocesses, such as, for example, electroplating.

In some embodiments folded portions 226, 230 and/or inner surfaces 234,236 are subjected to both an additive surface treatment process and asubtractive surface treatment process. For example, a material can beadded to folded portion 226, 230 and/or inner surface 234, 236 using anadditive surface treatment process and then part of the added materialcan be taken away using a subtractive surface treatment process.

Previous battery designs have incorporated small tabs extending from theelectrodes to transfer current between the electrodes and the electricload applied to the battery. The tabs provide a relatively smallcross-sectional area through which current must pass. Because directcurrent is passed through the entire cross-sectional area of aconductive path, a reduction in the cross-sectional area tends togenerate a greater amount of heat. Accordingly, the current density andlocalized heating in such previous battery designs is highest throughthe tabs. In some high-power and energy-dense batteries, hot spots format and around the tabs due to the tabs not being able to efficientlytransfer the amount of current provided to the load. Instead of tabs,battery 200 incorporates folded portion 226, 230 to transfer currentbetween electrode 210, 212 and end cap 206, 208. The increased contactsurface area between folded portion 226, 230 and end cap 206, 208,discussed in detail above, allows for uniform and efficient current flowbetween electrode 210, 212 and end cap 206, 208 and prevents significanthot spots from forming in battery 200. Accordingly, battery 200 issignificantly more thermally efficient than previous designs.

As previously mentioned, jacket 202 is comprised of a non-conductivematerial. In some embodiments, such as illustrated in FIGS. 1 and 6,jacket 202 can be a flexible tape or wrap that is wrapped around cell204 and end caps 206, 208 to couple end caps 206, 208 to cell 204.Specifically, in some embodiments, jacket 202 is a flexible polymer thatis wrapped around cell 204 and endcaps 206, 208. The flexible polymercan be made from any of a number of suitable polymers, such as, forexample, PTFE. End caps 206, 208 can further comprise a polyolefinrubber o-ring 238 configured to seal a space between end cap 206, 208and jacket 202. Battery 200 comprises an electrolyte fluid, and o-ring238 is configured to seal a space between end cap 206, 208 and jacket202 to seal the electrolyte fluid with an interior of jacket 202.

Referring to FIG. 7, in some embodiments, battery 200 has a rigid jacket203 that can be a rigid tube made from a non-conductive material. Insome embodiments, jacket 203 can be a rigid tube made from a polymersuch as, for example, PVC or HDPE. O-ring 238 is configured to seal aspace between end cap 206, 208 and jacket 203 to seal the electrolytefluid within an interior of jacket 203.

Referring to FIG. 8, a method 300 of assembling battery 200 isdescribed. Method 300 can begin at block 302 by layering a first and asecond electrode in a first direction. For example, the first electrodecan be anode 210 and the second electrode can be cathode 212 layered indirection 225, as described in FIGS. 3 and 4. The electrodes 210, 212can be layered to form anode extension end 222 and cathode extension end224. Method 300 can continue at block 304 by winding first and secondelectrodes 210, 212 about axis 218 to form rolled cell 204.

Method 300 can continue at block 306 by folding a portion of an edge ofthe first electrode. In method 300, the first electrode will bedescribed as anode 210 and the second electrode will be described ascathode 212, although one with skill in the art will recognize that thealternative is another embodiment. Accordingly, at block 306, anodefolded portion 226 and separator folded portion 228 can be folded.Method 300 can optionally continue at block 308 by folding cathodefolded portion 230 and separator folded portion 232. One with skill inthe art will understand that folding of folded portions 226, 230 can beperformed using any of a number of processes. For example, in someembodiments, a person or machine can fold folded portion 226, 230 bypressing the folded portion 226, 230 along axis 218 toward primarysection 220. In some embodiments, end caps 206, 208 can be used to foldfolded portions 226, 230. For example, a machine or person can press endcap 206, 208 against folded portion 226, 230 along axis 218 towardprimary section 220 to fold folded portion 226, 230 toward primarysection 220.

Method 300 can continue at block 310 by optionally performing a surfacetreatment process to anode folded portion 226. The surface treatmentprocess can be applied to one or all surfaces of folded portion 226. Thesurface treatment process can be a process that increases the surfacearea of folded portion 226, such as the additive and/or subtractivesurface treatment processes previously described. Optionally, a surfacetreatment process may also be applied to cathode folded portion 230, andcan be applied in a same or a substantially similar manner as what hasbeen previously described. One with skill in the art will recognize thatthe surface treatment process is not limited to being performed afterthe cell 204 is rolled or after folded portion 226 is folded. Forexample, in some embodiments, the surface treatment process can beapplied to folded portion 226, 230 before electrodes 210, 212 arelayered in block 302.

Method 300 can continue at block 312 by providing a first end cap forcontacting the first electrode, such as anode end cap 206 which contactsanode folded portion 226. Optionally, a surface treatment process can beapplied to inner surface 234 of end cap 206, which contacts foldedportion 226. The surface treatment process can be a process thatincreases the surfaces area of inner surface 234, such as the additiveor subtractive surface treatment processes previously described. Method300 can optionally continue at block 314 by providing cathode end cap208 for contacting cathode folded portion 230. As describe with anodeend cap 206, optionally, a surface treatment process can be applied toan inner surface 236 of end cap 208 to increase the surface area ofinner surface 236, such as the additive or subtractive surface treatmentprocesses previously described.

Method 300 can continue at block 316 by coupling anode end cap 206 tocell 204 to contact folded portion 226, such as, for example, withjacket 202 or 203. Method 300 can optionally continue at block 318 bycoupling cathode end cap 208 to cell 204 to contact cathode foldedportion 230, such as, for example, with jacket 202 or 203.

Referring to FIG. 9, a method of assembling a battery 200 with aflexible jacket 202 will be described. Method 400 can begin at block 402by winding first and second electrodes 210, 212 about an axis 218 toform a rolled cell 204. For example, cell 204 can be formed by themethods and process discussed in method 300. For method 400, the firstelectrode will be described as anode 210 and the second electrode willbe described as cathode 212, although one with skill in the art willrecognize that the alternative is another embodiment.

Method 400 can continue at block 404 by at least partially wrappingflexible jacket 202 around an outer circumferential surface of cell 204about axis 218. For example, flexible jacket 202 can be coupled to outerseparator 216 and wrapped about axis 218 to at least partially cover theouter circumferential surface of outer separator 216. As previouslydiscussed, flexible jacket 202 can be a flexible polymer made from anyof a number of suitable polymers, such as, for example, PTFE.

Method 400 can continue at block 406 by coupling first end cap 206 tocontact first electrode folded portion 226. For example, flexible jacket202 can be wrapped around end cap 206 and cell 204 to hold end cap 206against folded portion 226.

Method 400 can continue at block 408 by inserting an electrolyte fluidinto an interior of jacket 202. For example, jacket 202 can be wrappedaround cell 204 to form a generally cylindrical shape, and theelectrolyte fluid can be inserted into the interior of thecylindrically-shaped jacket 202.

Method 400 can continue at block 410 by coupling second end cap 208 to asecond end of cell 204 to contact second electrode folded portion 230.For example, flexible jacket 202 can be wrapped around end cap 208 andcell 204 to hold end cap 208 against folded portion 230.

Method 400 can continue at block 412 by wrapping flexible jacket 202around cell 204 about axis 218. Optionally, the wrapping in block 412can be performed with an increased tension, to more tightly wrap jacket202 around cell 204, than the wrapping performed at block 404.

Method 400 can continue at block 414 by performing a heat-shrink processto flexible jacket 202. Battery 200 can be heated so that flexiblejacket 202 shrinks to tightly form around cell 204 and end caps 206, 208to couple the components together. The heat-shrink process causes jacket202 to tightly seal with o-rings 238 of end caps 206, 208 against jacket202 to seal the electrolyte fluid within an interior of jacket 202. Insome embodiment, battery 200 can be disposed in a heat-shrink tube whichheats battery 200 to shrink jacket 202 as previously described.

Referring to FIG. 10, a method of assembling a battery 200 with a rigidjacket 203 will be described. Method 500 can begin at block 502 bywinding first and second electrodes 210, 212 about an axis 218 to form arolled cell 204. For example, cell 204 can be formed by the processesand methods discussed in methods 300. For method 500, the firstelectrode will be described as anode 210 and the second electrode willbe described as cathode 212, although one with skill in the art willrecognize that the alternative is another embodiment.

Method 500 can continue at block 504 by inserting cell 204 into jacket203. As previously discussed, flexible jacket 202 can be a rigid,cylindrically-shaped tube made from a non-conductive material. In someembodiments, jacket 203 can be a rigid tube made from a polymer, suchas, for example, PVC or HDPE.

Method 500 can continue at block 506 by coupling first end cap 206 to afirst end of jacket 203 to contact first electrode 210 and to seal thefirst end of 203. As illustrated in FIG. 7, cylindrically-shaped firstend cap 206 can be inserted into a first end of jacket 203 to contactfirst electrode folded portion 226. In some embodiments, o-ring 238 ofend cap 206 has a larger outer diameter than an inner diameter of theopening of 203, and insertion of end cap 206 into jacket 203 compresseso-ring 238 such that o-ring 238 seals a space between the outercircumferential surface of end cap 206 and the inner circumferentialsurface of 203. Method 500 can continue at block 508 by inserting anelectrolyte fluid into an interior of 203.

Method 500 can continue at block 510 by coupling second end cap 208 to asecond end of jacket 203 to contact second electrode 212 and to seal thesecond end of jacket 203. As illustrated in FIG. 7, cylindrically-shapedsecond end cap 208 can be inserted into a first end of jacket 203 tocontact second electrode folded portion 230. In some embodiments, o-ring238 of end cap 208 has a larger outer diameter than an inner diameter ofthe opening of jacket 203, and insertion of end cap 208 into jacket 203compresses o-ring 238 such that o-ring 238 seals a space between theouter circumferential surface of end cap 208 and the innercircumferential surface of jacket 203.

One with skill in the art will understand that, according to variousembodiments of this disclosure, portions of methods 300, 400, and/or 500can be combined to assemble battery 200 of this disclosure.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k isa variable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent,96 percent, 97 percent, 98 percent, 99 percent, or 100 percent.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed. Use of the term “optionally” withrespect to any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of. Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present invention.

What is claimed is:
 1. A battery cell assembly, comprising: a rolledcell formed from a first electrode and a second electrode rolledtogether about a longitudinal axis, the rolled cell comprising: aprimary section in which the first electrode and the second electrodeoverlap in a radial direction from the longitudinal axis; and a firstextension end extending from a first longitudinal end of the primarysection and formed from a first edge section of the first electrode,wherein the first edge section comprises a first folded portion foldedto contact an adjacent portion of the first edge section; and a firstend cap coupled to the rolled cell and contacting the first foldedportion.
 2. The battery cell assembly of claim 1, wherein a surface ofthe first folded portion contacting the first end cap has undergone asubtractive surface treatment process.
 3. The battery cell assembly ofclaim 1, wherein a surface of the first end cap contacting the firstfolded portion has undergone a subtractive surface treatment process. 4.The battery cell assembly of claim 1, further comprising a separatordisposed between the first electrode and the second electrode.
 5. Thebattery cell assembly of claim 1, further comprising a separatordisposed between the first electrode and the second electrode, whereinthe first extension end is further formed of an edge section of theseparator.
 6. The battery cell assembly of claim 5, wherein the edgesection of the separator comprises a separator folded portion disposedbetween the first folded portion and the primary section.
 7. The batterycell assembly of claim 1, wherein: the rolled cell further comprises asecond extension end formed on a second longitudinal end of the primarysection from a second edge section of the second electrode, wherein thesecond edge section includes a second folded portion folded to contactan adjacent portion of the second edge section; and the battery cellassembly further comprises a second end cap coupled to the rolled celland contacting the second folded portion.
 8. The battery cell assemblyof claim 1, further comprising a jacket configured to couple the firstend cap to the rolled cell, the jacket comprised of a non-conductivematerial.
 9. The battery cell assembly of claim 1, wherein a surface ofthe first folded portion contacting the first end cap has undergone anadditive surface treatment process.
 10. The battery cell assembly ofclaim 1, wherein a surface of the first end cap contacting the firstfolded portion has undergone an additive surface treatment process. 11.A method of assembling a battery cell assembly, comprising: layering afirst electrode with a second electrode in a first direction such that aprimary section of the first and second electrodes overlap in the firstdirection and a first edge section of the first electrode does notoverlap with the second electrode in the first direction; winding thefirst and second electrodes about an axis perpendicular to the firstdirection to form a cylindrically-shaped rolled cell with the first edgesection disposed on a first end of the rolled cell; folding a firstfolded portion of the first edge section to contact an adjacent portionof the first edge section; and coupling a first end cap to the rolledcell to contact the first folded portion.
 12. The method of claim 11,further comprising performing a subtractive surface treatment process toa surface of the first folded portion that contacts the first end cap.13. The method of claim 11, further comprising performing a subtractivesurface treatment process to a surface of the first end cap thatcontacts the first folded portion.
 14. The method of claim 11, whereinthe layering further comprises layering a separator between the firstelectrode and the second electrode in the first direction.
 15. Themethod of claim 11, wherein the layering further comprises layering aseparator between the first electrode and the second electrode in thefirst direction such that an edge section of the separator at leastpartially overlaps with the first edge section in the first directionand does not overlap with the second electrode in the first direction.16. The method of claim 15, wherein the folding further comprisesfolding the first folded portion such that a folded portion of the edgesection of the separator is disposed between the first folded portionand a primary section of the rolled cell.
 17. The method of claim 11,wherein: the layering further comprises layering the first electrode andthe second electrode such that a second edge section of the secondelectrode does not overlap with the first electrode in the firstdirection; the winding forms the rolled cell with the second edgesection disposed on a second end of the rolled cell; and the methodfurther comprises: folding a second folded portion of the second edgesection to contact an adjacent portion of the second edge section; andcoupling a second end cap to the rolled cell to contact the secondfolded portion.
 18. The method of claim 11, wherein the coupling furthercomprises coupling the first end cap to the rolled cell with a jacketcomprised of a non-conductive material.
 19. The method of claim 11,further comprising performing an additive surface treatment process to asurface of the first folded portion that contacts the first end cap. 20.The method of claim 11, further comprising performing an additivesurface treatment process to a surface of the first end cap thatcontacts the first folded portion.